High voltage power supply system for cathode ray tubes employing protective time delay means



Feb 5, w63 SATOSHI SHIMADA 3,3585

HIGH VOLTAGE POWER SUPPLY SYSTEM FOR CATHODE RAY TUBES EMPLOYING PROTECTIVE TIME DELAY MEANS Filed Aug. 5, 196s SIGNAL www f POWER SUPPLY VERTICAL AMPLIFIER l5 To SCREE N VOLT/IfirE POWER: S U PPL Y Tin/1E SYNCRO- CIRCUIT AMPLlFlC/ITION CIRCUIT HORI ZoNT/ll MULTIVIBR/IWR United States Patent Otitice 3,368,105 Patented Feb. 6, 1968 3,368,105 HIGH VOLTAGE POWER SUPPLY SYSTEM FOR CATHODE RAY TUBES EMPLOYING PROTEC- 'FIVE TIME DELAY MEANS Satoshi Shimada, Ohta-ku, Tokyo, Japan, assignor to Sony Corporation, Shinagawa-ku, Tokyo, Japan, a corporation of Japan Filed Aug. 5, 1963, Ser. No. 299,974 4 Claims. (Cl. 315-14) This invention was evolved with the general object of increasing the eiiiciency and prolonging the life of postacceleration or focusing type cathode ray tubes, such as Chromatron tubes, although it will be understood that various features of the invention have other applications.

lT his invention is based in part upon the discovery that power supply systems of the prior ait tend to cause premature failure of such cathode ray tubes because they allow excessive potentials to develop between closely spaced electrodes during the starting period. In a Chromatron tube, the back of a layer of phosphors making up the screen is covered with a metallic film which is electrified to a high potential, approximately 20,000 volts, during operation. A pair of tine grids of conducting wire, which serve to deect the electron beam according to the color signals received, is placed behind and in close proximity to the metallic film covering the phosphors on the tube face. A potential of between 1/s to 1/3 of that applied to the metallic film is applied to these grids under normal operating conditions. The difference in potential, 2/3 to of that applied to the metallic film, between the grids and the metallic film will not damage the tube under normal steady state operation.

It has been found that Chromatron tubes connected to a circuit designed according to the prior art may be damaged during the transient starting up period because the prior circuits allowed the metallic film to reach its operating potential, approximately 20,000 volts, while the grids remained at a relatively low potential. The resultant electrostatic forces were strong ennough to cause the metallic film to be pulled from the `face and accelerated into the grid where it could cause breakage or become an obstacle in the path of the electron beam. In some cases it caused the phosphorescent screen to come olf the face of the tube.

According to this invention, the potentials applied to the closely spaced electrodes of an electron tube such as a Chromatron are derived from circuits whose starting time constants are so matched that an excessive voltage difference between closely spaced electrodes cannot be realized during the transient start up periods.

Specific features of the invention reside in circuits which are comparatively simple and economical in construction and operation while providing the proper start ing time characteristics in a highly reliable and efficient manner. i

This invention contemplates other objects, features and advantages which will become more fully apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate a preferred embodiment and in which:

FIGURE l is a schematic electrical diagram illustrating a color television reproducing system constructed according to the principles of this invention;

FIGURE 2 is a graph of the potentials appearing at and between the metallic film and grids of a Chromatron connected to the circuit utilizing the prior art during the starting period; `and FIGURE 3 is a graph of the potentials appearing at and between the metallic film and grids of a Chromatron connected to the circuit utilizing this invention during the starting period.

FIGURE 1 illustrates a color television reproducing system generally `designated by the reference numeral 10. The system 10 comprises a signal amplification and detection circuit 11, a synchronization circuit 12, a vertical deflection circuit 13, a horizontal multivibrator circuit 14, and a Chromatron type cathode ray viewing tube 15, all of which are well known in the art. The system 10 also contains a color control circuit 16, prefer-ably of the type disclosed in my application for patent, Ser. No. 284,679, and a high voltage power supply and horizontal deflection circuit 17 which is the `subject of this invention.

The Chromatron tube 15, which is encircled by a deflection coil 18, contains an electron gun 1.9 and has a phosphorescent face 20 of the type required for reproduction of color television signals. Coated to the back of the phosphorescent face 20 is a metallic film 22. In close proximity to the metallic film is a pair of wire grids 23 which serve to control deflection of the electron beam toward the proper phosphors on the face 20 in accordance with the commands of the color control circuit 16.

When a high voltage power supply and horizontal deflection circuit of the prior art is substituted for the circuit 17 of this invention, the voltages las a function of time after start-up appearing upon the metallic film 22 and the grids 23 are shown by curves 24 and 25, respectively, of FIGURE 2.` The voltage applied to the metallic film 22 reaches its steady state value at a time t2 but the voltage at the grids 23 does not reach its steady state value until a time t3 which is longer than time t2. The voltage difference between the metallic film 22 and the grids 23, shown as a function of time by curve 26 of FIGURE 2, exceeds its steady state value after time t1 and reaches a maximum of nearly full anode potential at time t2 before dropping to its steady state value after time t3. The strong electrostatic forces caused by the high difference in potential between the electrodes at time t2 are the cause of tube damage.

The circuit 17 solves the problem of excessive interelectrode potentials by exploiting the difference in warmup characteristics of two different high voltage diode rectifiers, but other means can of course be utilized.

The circuit 17 contains a power amplifier vacuum tube 27 which has its control grid 28 connected to the horizontal multivibrator circuit 14 through a DC blocking capacitor 29, a resistor 30 being connected between the grid 2S and ground. A cathode 32 is grounded. The preferred embodiment utilizes a beam power pentode in which a pair of beam forming plates 33, diagrammatically illustrated as `a grid, are connected to the cathode. A positive potential of about volts is applied to a screen grid 34. Other amplification devices may be substituted without deviating from the scope and purpose of this invention. A plate 35 of the amplifier tube 27 is connected to a tap 36 of a primary Winding 37 of a transformer 3S, known in the art as `a horizontal flyback transformer. The circuit is connected to -a power supply of approximately 350 volts potential through a diode 40 which also serves, along with a capacitor 41, to damp out excessive oscillations. The cathode of the diode 40, which diode may be any type of electrical rectifying device but which is illustrated here as a vacuum tube diode, is connected to a tap 42 on the primary winding 37. Terminal 43 and a tap 44 are connected to the horizontal deflection coils of the deflection coil assembly 18 on the Chromatron tube 15. Tap 45 and terminal 46 are connected to anodes 47 and 48, respectively, of two specially chosen rectifiers 49 and 50, respectively', in a manner to be described. The location and connection of all the taps on the transformer 38 is made in a manner well known in the art.

In this embodiment, the transformer 38 is constructed so that the potential appearing between the tap 46 and directly heated cathode or heater cathode type of high :1

voltage vacuum diode rectifier such as a 3A3. It has a filament 51 which is encased in a cathode 52, a metallic sleeve fitted around the filament .and treated so .as to have a high electron emission at operating temperatures.

' The filament V53 of the'rectifier 49 is connected-to a secondary winding 54 on the transformer 38. Similarly,

`the filament 51 of the rectifier 50 is connected to `a secondary winding 55 on the transformer 38. The cathode 52 is connected to the filament 51.

The filament 53 of the rectifier 49 is connected to one end of .a filter capacitor 56 and one end of a potentiometer 57 which can be adjusted to set the voltage at the grid 23 to the desired level. The other ends of the capacitor 56 and potentiometer 57 are connected to ground.

A movable tap 58 of the potentiometer 57 is connected to a pair of balancing resistors 59 and 60 which couple the high voltage to the color control circuit 16 and the Y color control grids 23.

The cathode 52 of the rectifier 50 is connected to a filter capacitor 61 which is connected between the metallic film 22 and ground. The values of the capacitors 56 and 61 may be `chosen to control the time required -for the electrodes, here the metallic film 22 and the grids 23, to reach their steady state operating potential.

When the receiver 10 is turned on, the horizontal multivibrator circuit 14 transmits a saw-tooth signal to the grid 28 of the .amplifier tube 27 which in turn causes currents to fiow in the primary winding 37 of the transformer 38 in the manner well known in the art. The taps 4S and 46 reach operating potential almost immediately after the start-up period of the amplifier tube 27 and the diode 40 by reason of the autotransformer effect of the primary winding 37. The voltages appearing across the secondary windings 54 and 55 cause currents to ow in the filaments 53 and 51 respectively. The filament temperatures start to rise to operating levels, but because the filament 53 is smaller and lighter than the filament 51 and cathode 52, its instantaneous electron emission as a fraction of its steady state electron emission is higher than the comparative electron emission of the indirectly heated cathode S2 at al-l times during start-up. In other words, at any given time during the starting period, rectifier 49 conducts a higher percentage of its steady state current than does rectifier S0. This causes the capacitor 56 to charge up to operating potential at a faster rate than the capacitor 61, other factors being equal. The result is that the grids 23 of the Chromatron tube 15 reach 'operating potential before the metallic film 22.

In the preferred embodiment shown here, the control grids 23 reach operating potential, shown as a function of time in curve 62 of FIGURE 3, `at a time t1 while the metallic film reaches its operating potential at time t2', shown as a function of time by curve 63 of FIGURE 3. Because the voltage on the metallic film 22 is lless than the voltage on grids 23 before time t1' the maximum allowable interelectrode voltage is never exceeded and the tube is not subjected to excessive forces which cause premature failure. The potential between the metallic film 22 and the grids 23 as a function of time is shown by broken line curve 64 of FIGURE 3. As illustrated, a negative potential is applied from time to' to time t1 which ordinarily has no effect. However, if desired, the starting characteristics may be adjusted to obtain a potential which gradually rises to the steady state value as shown by the dotted line curve 65.

It will be apparent that the invention may be applied to electron tubes other than the Chromatron .and to other devices which Vrequire protection from excessive, inter-n electrode voltages during starting periods, and that other circuit arrangements and components may be employed to obtain starting characteristics such as to provide such protection.

It will be understood that many other modifications and variations fmay be effected without departing from the spirit and scope of the novel concepts of this invention.

What I claim is: v

1. Apparatus for supplying a first potential and a higher second potential to a first and second electrode of a postacceleration type cathode ray tube comprising first -and second power supplies Connected to a source of electrical energy of predetermined maximum potential for supplying the first and second potentials, respectively, said first and second power supplies having respectively associated therewith first and second time delay circuits, said two time delay circuits having time constants selected such that when said two power supplies are connected to said energy source the potential difference between said two electrodes is controlled and said apparatus may be operated without damage.

2. Apparatus `as recited in claim 1, wherein the tim delay of said second time delay circuit is `at least equal to that of said first time delay circuit.

3. Apparatus as recited in claim 1, wherein said two power supply circuits contain a first and second rectifier, respectively, said second rectifier having Ian indirectly heated cathode.

4. Apparatus yas recited in claim 3, wherein said first rectifier has a directly heated cathode.

References Cited UNITED STATES PATENTS 2,119,372 5/1938 Wendt 315-102 X 2,402,472 6/ 1946 Usselman 315-1102 X 2,749,474 6/ 1959 Preisig 315--14 2,879,444 3/1959 Nunan 315-14 OTHER REFERENCES RCA Victor Service Data for Color Television Receiver Model 2l-CT-55, 1954, No. T-13.

JOHN W. CALDWELL, Primary Examiner.

DAVID G. REDINBAUGH, Examiner.

T. A. GALLAGHER, R. L. RICHARDSON, Assistant Examiners. 

1. APPARATUS FOR SUPPLYING A FIRST POTENTIAL AND A HIGHER SECOND POTENTIAL TO A FIRST AND SECOND ELECTRODE OF A POSTACCELERATION TYPE CATHODE RAY TUBE COMPRISING FIRST AND SECOND POWER SUPPLIES CONNECTED TO A SOURCE OF ELECTRICAL ENERGY OF PREDETERMINED MAXIMUM POTENTIAL FOR SUPPLYING THE FIRST AND SECOND POTENTIALS, RESPECTIVELY, SAID FIRST AND SECOND POWER SUPPLIES HAVING RESPECTIVELY ASSOCIATED THEREWITH FIRST AND SECOND TIME DELAY CIRCUITS, SAID TWO TIME DELAY CIRCUITS HAVING TIME CONSTANTS SELECTED SUCH THAT WHEN SAID TWO POWER SUPPLIES ARE CONNECTED TO SAID ENERGY SOURCE THE POTENTIAL DIFFERENCE BETWEEN SAID TWO ELECTRODES IS CONTROLLED AND SAID APPARATUS MAY BE OPERATED WITHOUT DAMAGE. 